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Static electricity around us Where can static electricity be found in this lab scene? 3 of 38 © Boardworks Ltd 2007

Where does static electricity occur? What do the following familiar events have in common? l A lightning strike. l Dusters that attract dust. l Crackles when combing hair. l Cling film sticking to your hands. l Dust being attracted to television screens. l Clothes clinging to each other in a dryer. l Getting a shock after rubbing your feet on a carpet and then touching a metal object. All these events are due to static electricity. What causes static electricity to occur? 4 of 38 © Boardworks Ltd 2007

What is static electricity? Static electricity is due to the build up of electric charge. It is called ‘static’ electricity because the charge is unable to flow. The build up of electric charge can cause dangerous sparks. Sometimes, after walking on a carpet and then touching a metal object, such as a door knob, you might get a small shock. This is caused by static electricity. 5 of 38 © Boardworks Ltd 2007

Is lightning caused by electric charge? Lightning is an electric discharge that occurs when charge builds up in clouds. The physical properties of water enables regions of a cloud to become positivelyor negatively-charged. When enough charge has built up, it will follow a path to Earth. This movement produces lightning, which is simply a big spark! 6 of 38 © Boardworks Ltd 2007

What did Benjamin Franklin do? 7 of 38 © Boardworks Ltd 2007

Introducing static electricity – summary 8 of 38 © Boardworks Ltd 2007

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What causes static electricity? Static electricity is due to electric charge that builds up on the surface of an insulator, such as a plastic comb. The charge that has built up cannot easily flow away from the insulator, which is why it is called static electricity. 10 of 38 © Boardworks Ltd 2007

Where does static charge come from? All materials are made of atoms, which contain electric charges. Around the outside of an atom are electrons, which have a negative charge. The nucleus at the centre of an atom contains protons, which have a positive charge. An atom has equal amounts of negative and positive charges, which balance each other, so the atom has no overall charge. Electrons do not always stay attached to atoms and can sometimes be removed by rubbing. 11 of 38 © Boardworks Ltd 2007

How does static charge build up? Static charge can build up when two insulating materials are rubbed together, such as a plastic comb moving through hair. Friction between the materials causes electrons to be transferred from one material to the other: l One material ends up with more electrons, so it now has an overall negative charge. l One material ends up with fewer electrons, so it now has an overall positive charge. 12 of 38 © Boardworks Ltd 2007

How can static charge be created? Friction can be used to create a static charge. If an insulator is rubbed with a cloth, it can become charged in one of two ways: Electrons move from OR the cloth to the insulator. The insulator ends up with an overall negative charge. 13 of 38 Electrons move from the insulator to the cloth. The insulator ends up with an overall positive charge. © Boardworks Ltd 2007

Charging materials 14 of 38 © Boardworks Ltd 2007

Static charge – true or false? 15 of 38 © Boardworks Ltd 2007

How can static charge be detected? A gold leaf electroscope can be used to detect charge. An electroscope consists of an earthed metal case, inside which a metal rod is connected to a metal plate. A piece of gold leaf is attached to the other end of the metal rod. When the metal plate becomes charged, the charge spreads out through the metal rod and the gold leaf. The metal rod and the gold leaf gain the same charge, so the thin gold leaf is repelled from the rod and sticks out. 16 of 38 © Boardworks Ltd 2007

What is a Van de Graaff generator? A Van de Graaff generator is a machine used to build up static charge. It was invented in 1931 by Robert Jemison Van de Graaff, an American physicist. This machine uses the simple principle of rubbing insulating materials to build up a supply of charged particles. The generator can produce very high voltages and was first used to help scientists study the behaviour of subatomic particles. 17 of 38 © Boardworks Ltd 2007

‘Van de Graaff’ generator 18 of 38 © Boardworks Ltd 2007

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What are the forces between charges? The forces between charges can be investigated using rods made of insulating materials. acetate rods What happens when two positively-charged acetate rods are placed near each other? The rods repel each other because they have the same overall charge. What will happen if one rod is replaced with a charged polythene rod? 20 of 38 rods repel each other © Boardworks Ltd 2007

How do opposite charges behave? When a charged acetate rod is placed near a polythene charged polythene rod, rod the rods attract each other. acetate rod Why does this happen? The polythene rod has an overall positive charge and the acetate rod has an overall negative charge. The overall charges of these rods are opposite and so they attract each other. 21 of 38 rods attract each other © Boardworks Ltd 2007

Investigating pairs of charges 22 of 38 © Boardworks Ltd 2007

Experimenting with static charge 23 of 38 © Boardworks Ltd 2007

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How can static electricity be used? Static electricity has many uses, including: l photocopiers and laser printers l spray painting cars l filtering factory smoke l heart defibrillators 25 of 38 © Boardworks Ltd 2007

How does a photocopier work? 26 of 38 © Boardworks Ltd 2007

What happens in a photocopier? 27 of 38 © Boardworks Ltd 2007

How does spray painting cars work? 28 of 38 © Boardworks Ltd 2007

How does static charge reduce pollution? A precipitator in the chimney of a power station uses static electricity to filter smoke particles from waste gases. The smoke particles pass through a charged grid and pick up a negative charge. They are then attracted to the positively-charged collecting plates. The smoke particles lose their charge and fall back down the chimney, so the waste gases emitted are free of polluting smoke. 29 of 38 positivelycharged metal plates smoke particles metal grid at a high voltage © Boardworks Ltd 2007

How does a defibrillator work? A defibrillator is a machine that uses electricity to correct faulty heart rhythms. Fibrillation is an irregular heart rhythm, often brought on by a heart attack. The metal pads of the defibrillator are placed on the patient’s chest and then charged. This sends a controlled shock to the patient, which corrects the heart rhythm. 30 of 38 © Boardworks Ltd 2007

Uses of static electricity – summary 31 of 38 © Boardworks Ltd 2007

What are the dangers of static electricity? A build up of charge can produce sparks, which may lead to explosions and fire. Charge builds up when two insulators are rubbed together. This can occur when refuelling aircraft, when rolling paper in paper mills, and on grain shoots in grain stores. In paper mills, metal rollers are used to prevent the build up of charge. Metal grain shoots prevent fires in grain stores. Any charge is conducted away by the metal. How can explosions be prevented when refuelling aircraft? 32 of 38 © Boardworks Ltd 2007

How are planes refuelled safely? A build up of static charge when refuelling a plane could cause an explosion. This can be prevented by joining the delivery tanker and the fuel tank electrically with a metal wire. The wire provides a path for electricity to flow along, and so prevents the build up of any potentially dangerous static charge. 33 of 38 metal wire © Boardworks Ltd 2007

Static electricity – useful or a problem? 34 of 38 © Boardworks Ltd 2007

Glossary l attraction – The force between two objects with opposite overall charges, which pulls them together. l insulator – A material that does not conduct electricity. l lightning – A natural phenomenon that occurs because of a build up of charge in storm clouds. l repulsion – The force between two objects with the same overall charge, which pushes them apart. l static charge – The build up of electric charge due to friction between objects. l Van de Graaff generator – A scientific instrument that can be used to generate large quantities of charge. 36 of 38 © Boardworks Ltd 2007